The use of biomass in various further processing plants, for example in the production of biofuel or as fuel for a boiler, is an increasing trend. For example peat or other biomass that is relatively easy to process has been typically used in further processing plants. For collecting wood material that might otherwise be decomposed in forests, such as stumps and logging residues, for utilization, a favourable material for further processing is also so-called fuel wood, which has turned out to be more difficult to use than the materials used before.
A delivery of stumps and other fuel wood also often contains material that is problematic for the processing of the material, such as rocks of various sizes, sand and clay, which may cause various problems in the further processing plants. The rocks, sand, clay, and other similar non-combustible material may be conveyed as loose material with the stumps and other combustible fuel wood, and furthermore, for example rocks may also be found partly or totally inside a stump. Said problematic materials also directly impair the production capacity; being non-combustible materials, they reduce the combustion capacity, for example, in boilers.
In the prior art, fuel wood has been primarily used as fuel for a boiler in such a way that the fuel wood has been supplied to be burnt in the boiler. However, a typical further processing plant is quite poorly resistant to relatively large rocks. For example in boilers, particularly detrimental problems are typically caused by non-combustible material clogging the grate or corresponding structures and the ash removal devices. In prior art, attempts have been made to avoid these problems by crushing the fuel wood and the large rocks conveyed with it before the further processing plant. Even in this way, the effect of the non-combustible material, such as rocks, clay or sand, on the production capacity cannot be reduced to a sufficient extent. Furthermore, large rocks may break said crusher or increase the need for its maintenance.
Yet another problem in the utilization of biomass as a source of energy for the further processing plant lies in the fact that the dry matter content of the biomass supplied to the further processing plant may, at times, be so low that the utilization of said biofuel is no longer economically viable. For example, the use of particularly moist fuel wood as the fuel is not economically viable in general, particularly in boilers.
At the moment, there is no proper quality control system for the supply of biomass that contains fuel wood, to encourage the suppliers of biomass to supply material of highest possible quality for further processing. Instead, the present system, in which the price paid for biomass is typically directly proportional to the total weight of a load, does not take into account the fact that the load of biomass also contains particularly heavy non-combustible or otherwise unsuitable material, such as wet wood material or rocks.
For performing quality control in a laboratory, a small sample is often analyzed, which should represent a load delivered to be processed or crushed. However, such an analysis rarely depicts the quality of the load in reality, among other things because it is not possible in practice to take a representative sample of a load that contains, for example, large stumps and stump parts, to depict the quality of the whole load. Furthermore, analysing such a sample normally takes at least a day and requires separate work. For these reasons, the level of quality control according to the prior art typically remains relatively poor.
In practice, the method according to the prior art may lead to a situation in which the further utilization of biomass, particularly fuel wood, for example as fuel for boilers or in the preparation of biofuel, is not necessarily cost-effective or even economically viable.
Thus, a need exists in industry for a solution to the above-mentioned problem in such a way that the quality of supplied biomass could be controlled more efficiently than in the prior art.